ci: update to gagen 0.3 for maintainable pinning of all workflow dependencies (#33082)
Alternative to part of https://github.com/denoland/deno/pull/33054
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Co-authored-by: Bartek IwaĆczuk <biwanczuk@gmail.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>